On Mon, 7 Jul 2008 23:27:43 -0400, "Tom Gardner"
wrote:

In this pic, you can see a cam that operates a lever that is part of a wire
cutter. This is an old pic and we now use a roller instead of a cam but the
chain drive is the same. I want to replace this whole drive mechanism with an
air cylinder to move that lever. I roughly figure a 2" bore x 1" stroke will
have enough guts.

http://metalworking.com/Dropbox/_200...ob290-head.JPG

I need the cut timed within one degree of rotation of the same 1" shaft that
drives the chain. I want to be able to easily adjust the timing and have
adjustable dwell. Is there an off-shelf item to do this? I will need two
separate operation switches on the shaft.

There's this...
http://www.candycontrols.com/Switch/Switch_EMM.htm
and I know I've seen other brands, but can't think of the names right
now.

The traditional way to adjust the timing and dwell of a cam is to use
a pair of plate cams sandwiched together by a clamping hub. Here's a
photo of a camshaft on a spring winding machine I tooled up. Someone
else made the fancy graduated hubs - I doubt anyone ever really looked
at the numbers.
http://www.suscom-maine.net/~nsimmon...leeperCams.jpg

If you can get away with a homing routine at startup, a quadrature
counter or a cheap PLC and an encoder would also work. If you're sure
the shaft will never turn backwards, then the quadrature is
unecessary.

--
Ned Simmons